1. Field of the Invention
The present invention relates to an organic electro-luminescent display (OLED) device and a method of fabricating the same. More particularly, the present invention relates to an organic electro-luminescent display device without a protection layer and a method of fabricating the same.
2. Description of Related Art
Nowadays, the information communication industry has become a mainstream industry, and especially various portable communication display products have been a point of development. As the flat panel display is one of the communication interfaces between human and information device, its development is particularly important. The organic electro-luminescent display (OELD) has great potential due to its advantages of self-luminescence, wide viewing angle, power-saving, simple process, low cost, wide range of operating temperature, high response speed, full colorization, etc.; thus it is expected to be the mainstream of the next-generation flat panel displays.
The OLED is a display using a self-luminescence property of an organic luminescent material to achieve a display effect, and can be classified into one of the two types, namely a small molecule OELD (SM-OELD) and a polymer electro-luminescent device (PELD), according to the molecular weight of the organic luminescent material. The luminescent structure of the above two class includes a pair of electrodes and an organic material layer. When a direct current voltage is applied, electron-holes are injected into the organic luminescent material layer from the anode, and electrons are injected into the organic luminescent material layer from the cathode. Because a potential difference is caused by an applied electric field, the two kinds of carriers, electron-holes and electrons, move and generate radiative recombination in the organic luminescent material layer. A portion of the energy released by the recombination of electrons and electron-holes excites the molecules of the organic luminescent material to form singlet excited state molecules. When the singlet excited state molecules release energy and return to a ground state, a certain proportion of energy is released in a manner of photons to luminescence, which is the luminescence principle of the OLED.
FIG. 1 shows a schematic sectional view of a conventional active matrix OLED. Referring to FIG. 1, a pixel structure 100 of a conventional OLED is controlled by a scan line (not shown) and a data line (not shown) on a substrate 110. The pixel structure 100 mainly includes a switch thin film transistor (switch TFT) 120, a driving thin film transistor (driving TFT) 130, and an organic electro-luminescent unit 140.
Generally, when the pixel structure 100 of the OLED is fabricated, gates 121 and 131 are first formed on the substrate 110. The gates 121 and 131 may comprise, for example, a transparent conductive material, such as indium tin oxide (ITO). Thereafter, a gate insulator 112 is formed on the substrate 110. The gate insulator 112 covers the gates 121 and 131, and has a contact window opening 112a that expose a portion of the gate 131. Then, a source 122 and a drain 123 are formed at predetermined regions on the gate insulator 112 corresponding to the gate 121. Also, a source 132 and a drain 133 are formed at predetermined regions on the gate insulator 112 corresponding to the gate 131. The drain 123 of the switch thin film transistor is electrically connected to the gate 131 of the driving thin film transistor 130 through the contact window opening 112a. Further, a portion of the drain 133 extending rightward is used as an anode 141 of the organic electro-luminescent unit 140.
Thereafter, organic channel layers 124 and 134 are formed. The organic channel layer 124 covers a portion of the source 122 and drain 123, while the organic channel layer 134 covers a portion of the source 132 and drain 133. Further, the organic channel layers 124 and 134 comprise, for example, pentacene. Next, a protection layer 150 is formed on the switch thin film transistor 120 and the driving thin film transistor 130, to protect the switch thin film transistor 120 and the driving thin film transistor 130 from being adversely affected by moisture. The protection layer 150 has a contact window opening 150a corresponding to the anode 141. A luminescent layer 142 is formed in the contact window opening 150a. Thereafter, a metal layer 160 is formed on the protection layer 150 as a cathode 143 of the organic electro-luminescent unit 140. Thus, the fabrication of the pixel structure 100 of the OLED is completed.
However, when an organic material is used to form the above-mentioned protection layer 150, since the organic material can be patterned by a yellow light process, it is difficult to expose the anode 141 of the organic electro-luminescent unit 140. Further, when the organic material is etched to form the contact window opening 150a, the properties of the thin film transistor device are easily degraded.
In addition, since the properties of ordinary organic materials may be easily affected by moisture or atmospheric oxygen, their luminescence properties may be adversely affected. Therefore, when an OLED is packaged, usually an additional layer of hygroscopic material is added in order to prevent the organic material layer from being adversely affected by the moisture or atmospheric oxygen. However, this will increase the complexity of the package process.